A USC study finds that together, genetics and years of education can influence whether or not someone becomes obese. In 1972, England, Scotland and Wales raised the mandatory school attendance age from 15 to 16. Through a large-scale genetic study, USC Dornsife researchers have found that decades later, the change had a health benefit for those students affected by the reform, especially those who were at greatest risk of becoming obese. The research team found that the extra year of education contributed to weight loss, despite their genetic risk.

Both early-life experiences such as education and genetic factors are independently associated with later health, and a growing body of research suggests that health may also depend on the interaction between these two factors. But the results of studies examining gene-by-environment interactions have had limited replicability due in part to low statistical power resulting from analyses typically restricted to individual candidate genes.

To overcome this challenge, Silvia Barcellos, Leandro Carvalho, and Patrick Turley combined a large-scale natural experiment that generated variation in secondary education with polygenic scores, which are indices constructed from millions of genetic markers. The authors took advantage of a 1972 United Kingdom reform that increased the minimum age at which students could drop out of school from 15 to 16 years. Using middle-age health data from the UK Biobank, which stores the genomes of 500,000 people in the UK, the authors analyzed lung function, blood pressure, and a body size index encompassing body-mass index, body fat percentage, and waist-hip ratio for all quarter of a million individuals in the database. In addition, the authors used pre-existing data to construct polygenic scores for body-mass index.

The researchers found that the additional year of schooling produced a greater improvement in health, particularly in body size and lung function, in individuals genetically predisposed to a higher body-mass index than in individuals genetically predisposed to a lower body-mass index. Before the mandatory attendance age was changed, 31 out of every 100 people with the highest genetic-risk had an unhealthy body size. After the reform, the rate dropped to 18 out of every 100. Among those with the lowest risk, the rate remained roughly unchanged.

These findings were published in the journal Proceedings of the National Academy of Sciences. The study is the latest in a series by the USC Dornsife CESR researchers that examines how the 1972 change in the mandatory attendance age has affected other life outcomes for the affected students, such as whether they went to college or completed advance degrees, what incomes they earned and their socioeconomic status. In a previous blogpost we reported on other results of this study, which showed that the policy change in England improved health by reducing body fat and lung conditions, but it also increased blood pressure.

The findings show that genes alone do not determine who will become obese. In fact, in this case, one more year of high school lowered the influence of genes on whether someone becomes obese.

The results challenge the notion of genetic determinism. They suggest education reduced the role genes played in determining who became obese. Now, we are left with the question of why we observe larger health improvements for those with a higher genetic predisposition to obesity.